Preparation of CuMgAl hydrotalcite-like compounds at low MII/MIII molar ratios

CuMgAl hydrotalcite-like compounds with M-II/M-III=1 and Cu/Mg molar ratios 3:1, 1:1, 1:3 and 1:19 were synthesized by coprecipitation and characterized by elemental analyses, XRD, SEM, FT-IR, TG-DTA and BET surface area test. XRD of all samples showed that Cu/Mg/Al hydrotalcites without any detectable impurity phase could be obtained at Cu/Mg molar ratios 1:3 and 1:19, however, at high Cu/Mg molar ratios 3:1 and 1:1, Al(OH)(3) and copper hydroxides or oxides were obtained in the products besides the hydrotalcites, owing to the strong Jahn-Teller effect Of Cu2+. It was also found that the crystallinity of the solids increased with an increase in copper content. IR results showed that the symmetry of carbonate was reduced from D-3h to lower symmetry at high copper content. The thermal stability of the compounds decreased with increasing copper content, as indicated by TG-DTA measurements. Further thermal decomposition analyses showed that the surface area reached the maximum at calcination temperature of 500 degrees C and mixed metal oxides with crystalline MgO, amorphous Al2O3 and highly dispersed CuO were obtained.